The present invention relates to a method and an optical measuring device. It finds applications in particular in microscopy, for example in the field of biology and the acquisition of biological information from optical observation.
A microscope is an optical instrument generally used to view, analyze or measure objects too small for the naked eye.
We use the term biological to describe any biological entity in life sciences, regardless of its origin, human, animal or vegetal and of the purpose of the observation, be it for research, diagnostic or therapeutic application. This term includes the medical uses of the method described. Microscopy is used in the field of biology, for example, to observe, study and measure biological entities (objects) and their dynamics.
The usual definitions are used for: optical diffraction limit, Rayleigh criterion, Airy disk and its radius and diameter. We use in the context of the invention, the terms of superresolution, superresolved, superresolution imaging and superresolution microscopy to describe optical data acquisition, optical imaging and microscopy at a resolution higher than the optical diffraction limit. The usual definitions are used for fluorescence and for fluorophores.
Referring now to FIG. 1, which shows an illustration of the paradigm of Microscopy, 100, in the field of Biology.
Microscopy comprises the illumination, by a light source, not shown, using a microscope, 10, of a biological sample, 11, and the time-dependent measurement, using either visual observation or a detection module 12, of the light emitted by the sample.
The sample in Biology comprises a single—or a plurality—of different biological entities, 13 and 14, positioned at different positions.
Examples of such objects are, among others, a cell, a virus, a protein and a DNA fragment.
Fluorescence microscopy is one of the variants of microscopy, it has replaced in many biological applications, the other microscopy techniques.
A fluorescence microscope is an optical microscope used to study properties of organic or inorganic substances using the phenomena of fluorescence instead of, or in addition to other modalities such as reflection and absorption.
We refer again to FIG. 1, describing a fluorescence microscope; in fluorescence microscopy fluorophores, tiny point sources, 15 to 18, based on the physical phenomenon of one photon fluorescence, are fixed at specific positions of predetermined biological objects, 13 and 14; the light emitted by the fluorophores is observed instead of observing the light emitted by the biological objects, 13 and 14, themselves.
The sample is illuminated by light of wavelength, or specific wavelengths, which is absorbed by the fluorophore, thereby inducing the emission of light at different, higher, wavelengths.
The illumination light is separated from the emitted fluorescence, which is lower, by the use of a spectral emission filter.
Fluorophores have become an important tool for the visualization of biological objects. The activity and the biological information including details above the limit of resolution of 200 nm are systematically viewed and measured using fluorescence microscopy. This resolution limit is derived from the Rayleigh criterion, which in the best case, reaches 200 nm in systems designed specifically. For a long time, until the emergence of superresolution techniques described below, it was assumed that optical techniques, including fluorescence microscopy, are unable to visualize details smaller than the Rayleigh criterion, which is about 200 nm.
However, other fundamental biological activities also occur at scales smaller than 200 nm in biological samples. At this level of spatial resolution, important phenomena can be observed: the biological processes at the scale of intracellular, cell information transfer, the folding and unfolding of the proteins and changes in the DNA and RNA. For example, the measurement of this intracellular information open new avenues for understanding the biological activity, and lead to progress in understanding and monitoring of research and medical diagnostics.
The main implementations of fluorescence microscopy, as described in detail in the literature, are the confocal microscope, often used in a scanning configuration or spinning disc microscope, and the wide-field imaging microscope.
Referring now to FIG. 2 which is a simplified representation of a confocal fluorescence microscope of the prior art 200.
A confocal fluorescence microscope, FIG. 2 is an optical instrument. Its main hardware components are shown in FIG. 2. They include:
a light source, 20,
an optomechanical frame not shown
a cube filter, 21,
a microscope objective 22, and,                a detector assembly, 23,        
a processing unit, not shown.
The light source 20, which may be an arc lamp or a laser, creates light energy necessary for fluorescence.
The Optomechanical frame, not shown, is the support of all the optical components and auxiliary optics and includes alignment capacities.
It also includes optical elements, not shown, capable of shaping the beam to allow its focus point of a minimum size by means of the microscope objective.
It can also comprise, in a confocal scanning fluorescence, a spatial or angular scanning mechanism, not shown, to change the position of the point source with respect to the object to be measured.
The scanning mechanism can alternatively                mechanically translate the object, for example by using a translation plate,        optically scan the beam on the object, for example using a set of galvanometric mirrors or acousto-optical translators, or        use any combination of these translation means, mechanical or optical.        
In a confocal scanning fluorescence, the information is collected point by point, using the scanning mechanism.
It can also comprise, in a rotating disk type confocal fluorescence, a rotating disc having a plurality of pinholes, allowing the simultaneous projection of a plurality of points. In a confocal fluorescence rotating disk, a set of points, corresponding to the pinhole is acquired at any time and the rotation of the disk allows to scan the entire surface of the sample for a given longitudinal position.
The cube of filters, 21, channels the different optical signals and avoids contamination of the fluorescence signal by the emission. The cube is composed of filters: excitation filter, 210 dichroic mirror, 2 11, and emission filter 212. The filters and the dichroic mirror are selected according to the wavelength of excitation and emission spectral characteristics of the fluorophore.
The microscope objective 22 focuses the light created by the source in the focal plane of the lens 24, a light distribution pattern of small size, the optimum light distribution consisting of the Airy disk. The microscope objective 22, also collects back fluorescent light emitted by the fluorophores.
For a confocal scanning fluorescence the system can be descanned, that is to say, the return light can pass through the scanning mechanism to compensate for the translation due to scanning.
A detector lens, 25, creates, in the image plane of the detector 26, a magnified image of the focal plane of the lens 24.
A confocal hole, 27, is theoretically placed in the image plane of the detector 26. In most practical systems, the confocal hole, 27, is placed in an intermediate imaging plane, not shown, and reimaged onto the image plane of the detector 26.
The assembly of the detector, 23, detects the fluorescent intensity in the overall illuminated volume, and converts it into digital signal. For a confocal scanning microscope, the detector assembly comprises a detector of a single element, such as a PMT or SPAD. For a confocal microscope using a rotary disc, the detector assembly is comprised of a matrix of detector elements, such as a CCD, a EMCCD, a CMOS or a matrix of SPAD.
All components mounted from the light source to the dichroic filter is the illumination path, 201. The detection channel, 202, represents all the components mounted from the dichroic filter to the assembly of the detector.
The elementary optical process of a confocal microscope can be segmented into six steps:
Projecting light on the volume analyzed                Fluorescent light emission by fluorophores        Imaging of the fluorophores in the focal plane        Limitation in the focal plane of light analyzed by confocal hole        Integration of light analyzed by a photoelectric detector        
Display of the measured intensity as a pixel value in an image
Fluorescence microscopes are available from several manufacturers, such as Nikon, Zeiss, Leica and Olympus. Fluorescence microscopes can be either standard microscopes suitable for fluorescence or microscopes optimized specifically for fluorescence. Modern microscopes are versatile instruments capable of operating in many different modalities, including, but not limited to, fluorescence modalities, using the same platform and most optomechanical components. Most fluorescence microscopes are developed as an open platform, capable of performing several additional features with minimal modifications. Other fluorescence microscopes are instruments dedicated, adapted for a specific task, such as medical diagnosis or pharmaceuticals.
New optical methods, methods for superresolution are capable of discriminating fluorophores, below the Rayleigh criterion. These methods are being developed by several companies, laboratories and researchers and some of the instruments using these methods, the superresolution microscopes, are commercially available. Several comparative analysis of superresolution methods have recently been published in the literature, such as the article written by Ricardo Henriques and Mr. Musa Mhlanga (“PALM and STORM: What hides beyond the Rayleigh limit?”, Biotechnology Journal, 4, 846-857 (2009)), or the article written by Kelly Rae Chi (“Super resolution microscopy: breaking the limits”, Nature Methods, 6, 15-18 (2008)).
An updated bibliography on the superresolution is on the website of the company Zeiss Co. (“Zeiss Microscopy and image analysis”, (2011), retrieved at http://www.zeiss.com/4125681C00466C26/?Open) and on the website of the company Nikon Co. (“MicroscopyU: the source for Microscopy Education” (2011) retrieved at http://www.microscopyu.com/).
Different existing methods of microscopy and existing microscopes, not incorporating the superresolution, allow microscopic observation up to the optical diffraction limit. This reduces their field of use to a limited set of applications.
New superresolution techniques allow to obtain information beyond the resolution limit. The main problem of all existing superresolution techniques is that the envelope of performance, expressed in terms of lateral resolution of longitudinal resolution, speed, light intensity necessary for phototoxicity in the biological object, of ability to measure different objects, is very limited.
In addition, most of the methods and instruments can provide superresolution either a good lateral resolution or a good longitudinal resolution, but rarely both.
In addition, all these instruments are complex and require a highly skilled operator.
In addition, these instruments can generally observe a small part of biological specimens due to strong operational limitations, such as, for some of them, a shallow depth of field or a requirement of very high light intensities, harmful to cells.
Another problem with the methods and instruments of super resolution, is that most of them are able to recover in the illuminated volume, the attributes of a single fluorophore, but fail to recognize the presence of simultaneously several fluorophores and measuring their attributes.
An additional problem with the methods and instruments of superresolution is that these methods and instruments are presented to users and perceived by them as a general tool, able to replace the standard or confocal microscopes. However, the methods and instruments superresolution lack the simplicity, robustness, ease of use and competitive prices of standard microscopes which hinders their use as research tools or as general diagnostic tools.
Another problem with existing superresolution methods and tools is that most of these methods and tools are designed as stand-alone instruments designed to replace standard microscopes. Such an approach requires the replacement of existing instruments and the renewal of all systems and devices all the knowledge and know-how related to microscopy platforms and developed over many years.
Another problem with most methods and instruments fluorescence microscopy and superresolution is that these methods and tools are designed on a paradigm of image acquisition, the entity for which basic information is—or more images, or—or more—ROI regions—Region Of Interest bi- or three-dimensional. Algorithmic, systemic and superresolution methods described later in the context of the invention will, by their inherent flexibility, the development of new strategies of acquisition. These acquisition procedures, dynamic and selective, will be defined by an optimized sequence acquisition and interactive and deferred processing. They allow a more sophisticated optimization of the useful information, as defined by criteria based on the shape, geometry and dynamics of one or more fluorescent objects, separately or relative one to the other.
So there is still an urgent need to provide superresolution methods and tools and algorithms methods capable of measuring with high accuracy the attributes of a fluorophore. It is also necessary to provide methods and tools to detect and quantify the presence of multiple fluorophores placed in the same volume illuminated.